Zothecula writes: Last year, NASA announced it was seeking proposals for mission concept studies of a high-power solar electric propulsion (SEP) system that could be used in a "space tugboat." Such a ship would be used ferry payloads in low Earth orbit (LEO) into higher energy orbits, including geosynchronous Earth orbit (GEO) and Lagrange point one (L1) — saving on fuel and the use of expensive secondary boosters. NASA also anticipates an SEP system could be used to propel spacecraft into deep space for science missions and for the placement, service, resupply, repositioning and salvaging of space assets by commercial operators.